Warm Air Ducts Ducts that distribute heated air to the house lose heat in two ways: • Heat flows from the heated duct walls to the colder surroundings • Heated air escapes from leaky supply duct joints and cold air is drawn into leaking return ducts. Both of these losses reduce the useful heat delivered to the house and increase fuel consumption. Warm air is lower in temperature than hot water, but the duct surface area is much larger. The large duct area and air leaks contribute to relatively high distribution system losses for warm air systems. Additionally, many warm air ducts pass through unheated areas, such as attics or crawl spaces. Because of the cooler surroundings, heat loss into these areas is large. Inspect all warm air ducts to determine if there are leaks that can be sealed. Properly sealed and insulated ducts can reduce cooling cost by up to 15% and heating by 20%! The furnace fan (blower) moves 1,200 cfm. Return leaks in the furnace room are a problem because the blower is strong enough to backdraft the burner. Water Heating The heat losses associated with direct-fired water heaters are the same losses any boiler suffers: On-cycle losses, idle (off-cycle) losses up the flue, infiltration losses, piping losses, jacket losses. The efficiency measurement for water heaters is the Energy Factor (EF). Energy Factor tells how effectively the heat from the energy source is transferred to the water and quantifies standby losses (the amount of heat lost per hour from the stored water compared to the heat content of the water) and cycling losses. The primary losses for oilfired water heaters 22 National Oilheat Research Alliance No Leaks Return Leaks Supply Leaks
NORA Advanced Efficiency
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